Any monochromatic spectral light that evokes the corresponding perception of hue
In color science, the dominant wavelength is a method of approximating a color's hue. Along with purity, it makes up one half of the Helmholtz coordinates. A color's dominant wavelength is the wavelength of monochromatic spectral light that, if plotted in a chromaticity diagram, the straight line that passes through the color in question and the white point will also pass through this wavelength.[1]
^Schanda, Janos (2007). Colorimetry : understanding the CIE system. [Vienna, Austria]: CIE/Commission internationale de l'eclairage. pp. 65–66. ISBN978-0-470-04904-4.